I think that if you forward those emails to the high school directors, you should also CC the question asker.
That email could look something like:
"Hey, that's a great question, but I'm not sure of the answer. I have CC'd the high school directors on this reply, and they'll be able to answer any questions you have about HS band."
That way, both parties know that the question was forwarded to the appropriate person, and that parent now has the correct emails to send questions to.
Use a generic response like this for every question, and I would assume that the HS directors would get the hint eventually.